A solar water heater in Cyprus warms 150 litres of water (150 kg) from 20 to 60 degrees Celsius. Water needs 4.2 kilojoules per kilogram per degree. How much energy is needed?
Answer and explanation
Correct answer: D. 25,200 kilojoules
- Step 1: Use energy = mass times 4.2 times the temperature rise. Step 2. The rise is 40 degrees, and 150 times 4.2 times 40 is 25,200. Answer: 25,200 kilojoules. Why not the others: 2,520 and 252,000 are errors of a factor of ten; 12,600 uses a rise of only 20 degrees.
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